Transdermal vehicle formulations are known and used for delivery of a variety of active agents. In veterinary applications, such formulations are often referred to as ‘pour on’ treatments. The transdermal route of administration is favourable as it minimises the amount of work required to deliver an agent or agents to an animal and avoids potential harm or danger in handling distressed animals. A further advantage of transdermal administration is that the dose can easily be metered, measured and delivered to the animal.
Despite the above advantages, transdermal methods of administration are rarely commercialised for use with woolly animals such as sheep and goats. This is because such animals present a major challenge for transdermal delivery as it is necessary to penetrate through not only the skin or epidermis but also diffuse the active agent through wool, dirt that is usually present on the wool, and then to also penetrate the sebum—mainly comprising lanolin in woolly animals. Lanolin is a highly difficult waxy substance to penetrate as it is highly immiscible with water and repels most agents and vehicle systems.
Art exists describing transdermal formulations for treatment of internal and external parasites in animals where different active ingredients from anthelmintic range are used. However, with the exception of cattle pour on's, few other pour on formulations have been commercialised and there remains a demand for a parasiticidal topically applied product, particularly for animals other than cattle.
Attempts have been made to develop reliable transdermal formulations suitable for woolly animal application, particularly for sheep and goats. These formulations typically have significant limitations in application timing and method. One example of an art composition commercialised in Australia is produced by Coopers, marketed under the brand Maverick™. This product is an endo-parasite transdermal formulation. The product has a number of limitations hence the uptake by the market has not been big with most farmers still preferring the difficulties of drenching sheep as opposed to using the Maverick™ product. By way of example, the Maverick™ product is recommended to be used only within 24 hours of shearing thereby severely limiting the window of application time. Further, a special applicator gun is needed in order to administer Maverick™. This greatly increases the cost and complexity to the farmer in using the product. The Maverick™ product is also a specialised micellar formulation that may require special manufacture and potentially expensive compounds to manufacture.
Further, as may be appreciated, it can be useful to combine two or more active agents in the one formulation. This can further complicate the formulation process for pour on design (for woolly and non-woolly animals) as different agents may have different characteristics such as varying miscibility. Patents that describe potential solutions to formulating multiple agents together include: NZ336139 that describes levamisole in an emulsion with ivermectin and albendazole and NZ507445 that describes a composition containing an antibiotic and an anthelmintic compound in the form of a suspension.
Production of emulsions or suspensions is not ideal since preparation of products containing different phases, such as solid/liquid or oil/water phases can be associated with significant manufacturing costs. For example, high shear dispensers and/or mills or homogenisers may be needed to produce the end product. Further, emulsions and suspensions can settle during storage and require the user to for example shake the product to re-suspend or, in worst cases, the agents will not re-mix resulting in ineffective products. In some cases, separation issues can result in short product storage time periods thereby limiting the usefulness of the product.
As should be appreciated from the above, there may be value in providing transdermal formulations that are simple to manufacture; minimise the amount of excipients used; are able to penetrate the skin barrier in an efficacious manner; deliver the agent or agents in a measurable and easily applied manner; and be able to deal with challenging conditions when the skin also has wool, dirt or sebum fats, oils or waxes present; or at least to provide the public with a choice.
Further aspects and advantages of the formulations, methods of treatment and use will become apparent from the ensuing description that is given by way of example only.